Micro-optic film materials for projecting synthetic images generally comprise (a) a light-transmitting polymeric substrate, (b) an arrangement of micro-sized image icons located on or within the polymeric substrate, and (c) an arrangement of focusing elements (e.g., microlenses). The image icon and focusing element arrangements are configured such that when the arrangement of image icons is viewed through the arrangement of focusing elements, one or more synthetic images are projected. These projected images may show a number of different optical effects. Material constructions capable of presenting such effects are described in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., U.S. Pat. No. 7,738,175 to Steenblik et al., U.S. Patent Application Publication No. 2009/0034082 to Commander et al., U.S. Patent Application Publication No. 2009/0008923 to Kaule et al.; U.S. Patent Application Publication No. 2010/0177094 to Kaule et al.; U.S. Patent Application Publication No. 2010/0182221 to Kaule et al.; European Patent Application No. 08784548.3 to Kaule et al.; and European Patent Application No. 08759342.2 to Kaule.
These film materials may be used as security devices for authentication of banknotes, secure documents and products. For banknotes and secure documents, these materials are typically used in the form of a strip or thread and either partially embedded within the banknote or document, or applied to a surface thereof. For passports or other identification (ID) documents, these materials could be used as a full laminate.
While such devices have been used in the past, they have not had, for example, a “peel to destroy” tamper indicating property. By tampering is meant unauthorized interference with the device (i.e., attempts to remove the device from an object) whether for the purposes of counterfeiting, forgery or substitution.
The present invention therefore provides a tamper indicating security device that operates to produce one or more synthetic images, the device being adhered or bonded to a base material (e.g., passport paper), wherein the device separates or delaminates when an attempt is made to detach the device from the base material, rendering the device either fully or partially inoperable. The phrase “fully or partially inoperable”, as used herein, is intended to mean that the inventive device would either (a) no longer be capable of producing one or more synthetic images (fully inoperable), or (b) only be capable of producing a reduced number of synthetic images (partially inoperable).
The tamper indicating security device of the present invention is changed irreversibly when removal of the device from an object is attempted. The device, therefore, cannot be removed and re-adhered to another object, such as a counterfeit object, without the replacement being detected.
The inventive device may be adhered or bonded to an underlying base material with or without the use of an adhesive. By way of example, bonding may be achieved using ultrasonic welding, vibration welding, and laser fusing of the device directly to the base material.
The tamper indicating security device of the present invention comprises an optical film material that is made up of at least one layer containing focusing elements (e.g., lenses), at least one layer containing image elements (e.g., icons), and at least one optical spacer or spacer layer positioned between the focusing element layer(s) and the image element layer(s), with the focusing elements forming one or more synthetic images of at least a portion of the image elements. The optical film material may optionally further comprise one or more layers selected from the group of bond weakening layers, primer or adhesive layers, and combinations thereof. Moreover, the focusing element layer(s) may optionally constitute a partially or fully embedded layer, as will be described in more detail below.
The inventive security device may optionally further comprise one or more layers applied to one or opposing sides of the device, those layers including, but not limited to, print layers (e.g., back side print layers), metalized and/or partially demetalized layers, primer or adhesive layers, sealing or coating layers, stiffening layers, and combinations thereof.
When the inventive device is adhered or bonded to a base material and an attempt is made to separate the device from the base material, the device is designed to fail, with failure generally occurring internally within and/or between the focusing element layer(s) and the image element layer(s).
Separation attempts can range from trying to pull the device from the base material, to trying to slide a sharp object, such as a razor blade, between the film material and the base material, to chemical, thermal, cryogenic, or mechanical shock.
In one contemplated embodiment, the optical film material further comprises an optical spacer or spacer layer. More specifically, the tamper indicating security device of this contemplated embodiment comprises:                (a) an optical film material comprising at least one layer containing focusing elements, at least one layer containing image elements, and an optical spacer or spacer layer positioned between and adhered to the at least one focusing element layer and the at least one image element layer, with the focusing elements forming one or more synthetic images of at least a portion of the image elements; and        (b) optionally, one or more layers selected from the group of print layers, metalized and/or partially demetalized layers, primer or adhesive layers, sealing or coating layers, stiffening layers, and combinations thereof.        
The tamper indicating security device of this contemplated embodiment may be designed for intralayer failure at any layer, or interlayer failure at any interface between the focusing element layer(s) and the image element layer(s) such as between the focusing element layer(s) and the optical spacer, or between the optical spacer and the image element layer(s) of the optical film material. In particular, when the device is adhered to a base material and an attempt is made to separate the device from the base material, the stress inherent in such an attempt will be concentrated at an interface of one set of these named layers.
In another contemplated embodiment, two optical spacer or spacer layers and a primer or adhesive layer are used in the optical film material. More specifically, the tamper indicating security device of this contemplated embodiment comprises:                (a) an optical film material comprising at least one layer containing focusing elements, at least one layer containing image elements, two optical spacer or spacer layers adhered together by a primer or adhesive layer, the two optical spacer or spacer layers positioned between and adhered to the at least one focusing element layer and the at least one image element layer, with the focusing elements forming one or more synthetic images of at least a portion of the image elements; and        (b) optionally, one or more layers selected from the group of print layers, metalized and/or partially demetalized layers, primer or adhesive layers, sealing or coating layers, stiffening layers, and combinations thereof.        
The tamper indicating security device of this contemplated embodiment may be designed for interlayer failure between one of the optical spacer or spacer layers and the primer or adhesive layer of the optical film material.
In yet another contemplated embodiment, a bond weakening layer is introduced into the optical film material, with failure designed to occur within this layer and/or between this layer and one or more adjacent or contiguous layers.
In yet a further contemplated embodiment, the focusing elements are reflective focusing elements or focusing reflectors, where interlayer failure may be designed to occur between, for example, a reflective (e.g., metal) layer applied to a surface of the focusing reflectors and the focusing reflectors, or between the optical spacer and the focusing reflectors.
To achieve the described intralayer and/or interlayer failure the inventive security device is designed such that:                (a) the cohesive strength of a target layer in the security device is less than the cohesive strength of the other layers in the security device; and/or        (b) the bond strength of a target interface between two layers in the security device is less than the bond strength(s) of the interface(s) between other layers in the security device and between the security device and the base material.        
As will be described in more detail below, the inventive security device may be designed to incorporate these relative cohesive and/or bond strengths, which contribute to intralayer failure and/or interlayer failure or delamination at a target layer or at a target interface between the focusing element layer(s) and the image element layer(s), by:                (1) increasing or decreasing the stiffness (Young's modulus or tensile modulus), bond strength, or crosslink density of one or more target layers or interfaces relative to the remaining layers or interfaces of the security device;        (2) incorporating stress inducing (e.g., volume changing) components into one or more target layers of the security device; and/or        (3) introducing a bond weakening layer at a target interface between two layers of the security device.        
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.